Year

1997

Degree Name

Doctor of Philosophy

Department

Department of Environmental Science

Abstract

The NOx and SOx emissions from iron ore sintering processes dominate the air pollutants emitted by an integrated steel works. Waste gases treatment technologies are applied in the traditional de-NOx, de-SOx processes. This study takes a different approach by investigating methods of depressing the NOx and SOx formation in the iron ore sintering stage rather than to treat the waste gases.

Our studies concluded that urea was a potential additive for in-system de-SOx. A 0.03 wt% of urea charging mass can lead to 85% SOx depression efficiency. A study of passing S02 through heated urea has shown that reaction compounds are ammonium sulfate and bisulfate. An FTIR analysis of suspended particles from the sinter pot waste gases also indicated that ammonium sulfate and bisulfate were formed when urea was added into the sinter mix.

The NOx emissions in the sintering process are mainly controlled by the combustion situation. Our studies confirmed that increasing the coke breeze combustion speed and shortening the high temperature duration time was a feasible countermeasure to depress the NOx formation. The granulation of the sinter raw mixture becomes important in improving the permeability of the sinter bed. Our studies showed that the use of sugar as an binding enhancer dramatically improved the sinter bed permeability and shortened the sintering time. The experimental results showed that a 1 wt% sugar addition to the sinter mix, shortened the sintering time from 23'50" to 19'16". The conversion ratio of nitrogen fragments to nitrogen oxides was significantly decreased, the emission mass decreased from 533.8 to 283.3g/t.sinter, and the emission concentration also reduced from 223 to 160 ppm (15 % O2 base). Because of the short sintering time, the sinter productivity also dramatically increased from 37.5 to 45.5 t/m2/24hr.

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